• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.1
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• pp.31-37
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• 2017

In this paper, computation results of reducible modeling, stress recovery and energy release rate were compared with the results of VABS, Virtual Crack Closure Technique. The result of stress recovery analysis for 1-D model including the stiffness matrix is compared with stress results of three-dimensional 3-D FEM. Energy release rate of composite beam with longitudinal cracks is calculated and compare verifications of numerical analysis results of 3-D FEM and VABS. The procedure of calculating energy release rate through dimensional reduction and stress recovery is intended to be efficient and be utilized in the life-cycle of high-altitude uav's wing, wind blades and tilt rotor blade.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.4
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• pp.600-613
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• 2015

The Fishing gear loss has been repeated every year in the West Sea; however, there has been no solution. So fisher men have undergone economic loss every year. Thus it is required to reduce the loss of fishing gear. In this study to find out the reason that the fishing gear is lost in the Sea, 10 years data of wave and current for 6 locations in the West Sea were investigated and a numerical modelling were conducted into the behaviour of a gillnet in wave and current. The fishing gear was modelled with the mass spring model. As a result, it came out into the open that the location where fishing gear loss occurred most frequently was Choongnam province. The height of the maximum significant wave in this province was 6.7 m and the period of that was 4.4 second. The maximum current speed was 0.7 m/s. As a result of simulation with these data, it was revealed that the buoy is one of the reasons to decrease the holding power of the gillnet. For example, the tension of anchor rope was decreased to 50% while the drag coefficient or volume of buoy was decreased to 25%. So it is predicted that an improvement of the buoy contributes to the reduction of the gillnet loss.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.53 no.4
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• pp.309-316
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• 2017

In this paper, numerical modeling is conducted to analyze the tension of an anchor line by varying the size and drag coefficient of a buoy when the trapnet is influenced by the wave and the current simultaneously. A mass-spring model was used to analyze the behavior of trapnet underwater under the influence of waves and current. In the simulation of numerical model, wave height of 3, 4, 5 and 6 m, a period of 4.4 s, and the flow speed of 0.7 m/s were used for the wave and current condition. The drag coefficients of buoy were 0.8, 0.4 and 0.2, respectively. The size of buoy was 100, 50 and 25% based on the cylindrical buoy ($0.0311m^3$) used for swimming crab trap. The drag coefficient of the trapnet, the main model for numerical analysis, was obtained by a circular water channel experiment using a 6-component load cell. As a result of the simulation, the tension of the anchor line decreased proportional to buoy's drag coefficient and size; the higher the wave height, the greater the decrease rate of the tension. When the buoy drag coefficient and size decreased to one fourth, the tension of the anchor line decreased to a half and the tension of the anchor line was lower than the holding power of the anchor even at 6 m of wave height. Therefore, reducing the buoy drag coefficient and size appropriately reduces the trapnet load from the wave, which also reduces the possibility of trapnet loss.

• Journal of Korean Society for Atmospheric Environment
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• v.26 no.6
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• pp.591-605
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• 2010

Recirculation of airmass in coastal region occurs because of the change from land to sea breeze and was shown to produce a contrary result on air quality. This study examines the numerical simulation to analyze the effect of recirculation flow in Gwangyang Bay, Korea. For this purpose two case studies are performed by the WRF-FLEXPART-CMAQ modeling system, each for a different Meso-Synoptic Index. Additionally this research make a comparative study of large domain (Domain L) and small domain (Domain S). The horizontal wind fields are simulated from WRF. Changes in the land-sea breeze have an effect on the particle dispersion modeling. The numerical simulation of air quality is carried out to investigate the recirculation of ozone. Ozone is transported to eastward under strong synoptic condition (Case_strong) because of westerly synoptic flow and this pattern can confirm in all domain. However ozone swept off by the land breeze and then transported to northward along sea breeze under conditions of clear sky and weak winds (Case_weak). In this case re-advected ozone isn't simulate in Domain S. The study found that recirculation of airmass must be concerned when numerical simulation of air quality is performed in coastal region, especially on a sunny day.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.4
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• pp.79-86
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• 2010

This research is a thing about reverse operation about the solar power for location decision and increasing efficiency of the solar power generation equipments. The purpose of this research is reverse operation about the amount of sunshine using the climate and spatial elements. Following the result of correlation analysis, the wind-speed and cloud-amount factor are excluded, because the correlation and significance coefficients are out of value. Each outcome of regression analysis using the other four climate elements, and regression analysis using spatial elements is what the amount of sunshine and the solar altitude are the most influence to the insolation-modeling. Doing the regression analysis based on the precedent result make the result that climate elements have bigger coefficient of regression than spatial elements. This outcome means the climate elements are more influence than spatial elements.

• Journal of Power Electronics
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• v.11 no.5
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• pp.759-766
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• 2011

This paper focuses on monitoring and predicting the short circuit faults of the rotor windings of large turbo-generator systems. For the purpose of increasing efficiency and decreasing maintenance cost, a method that combines the HHT (Hilbert Huang Transform) with a wavelet has been studied. This method is based on analyzing a classical Albright detecting coil. Due to the Empirical Mode Decomposition (EMD) and the Intrinsic Mode Functions (IMF) of the HHT the exact location of a short circuit of rotor windings may be given. However, a part of the useful information is eliminated by the unreasonable decomposing scale of the wavelet. Based on the thermodynamics modeling method, this study was illustrated with a 50MW turbo-generator system that is installed in Northern China. The analysis results, which have very good agreement with those of a previous study, show that the method of combining the HHT with a wavelet is an effective way to analyze and predict the short circuit faults of the rotor windings of large generators, such as supercritical turbo-generator systems and wind turbo-generator systems. This work can offer a useful reference for analyzing smart grids by improving the power quality of a distribution network that is supplied by a turbo-generator system.

• Journal of Aerospace System Engineering
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• v.16 no.4
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• pp.77-87
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• 2022

The Precision Aerial Delivery System is an instrument designed to improve the poor landing accuracy of aerial delivery system with conventional circular parachutes, and is equipped with an Airborne Guidance Unit to safely transport supplies to the desired destination. Currently, the landing accuracy of the PADS product is reported as CEP₅₀ 100m and also differs significantly, depending on the actual topography and weather environment. In this study, HILS was constructed based on the 6DOF nonlinear modeling of PADS to analyze the maneuver characteristics of Ram Air Parachute under wind environments. By using the new algorithm a precision soft landing algorithm including Energy Management and Final Approach is designed. HILS results show that it is possible to achieve a precise soft landing within CEP₅₀ 40m, and it can be exploited to develop an actual PADS drop test.

• Journal of the Korean Geotechnical Society
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• v.29 no.4
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• pp.23-32
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• 2013

In order to evaluate the bearing capacity behaviour of a monopod suction bucket foundation for an offshore wind tower at the western sea of Korea, a centrifuge load test and numerical analyses were performed. The monopod bucket foundation was designed to be installed in a silty sand layer. The model soil was prepared to simulate a target site by using soil samples having similar properties and controlling relative density. In-flight miniature cone penetration test and bender element array were used to confirm that the model soil had represented the target site conditions. The load - rotation curve of the centrifuge load test was analysed. A series of numerical analyses were performed to validate the experimental conditions. Self-weight of the model, distance to the boundary and elastic modulus of the soil layer were varied to study their effects on the load - rotation curves.

• Journal of Korean Society of Steel Construction
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• v.25 no.3
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• pp.307-320
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• 2013

This paper proposes a new hybrid support structure by the driven piles which removes disadvantages of the existing type of support structure for offshore wind turbines. The hybrid type of support structure is combined with concrete cone and steel shaft, and is supported not only by gravity type foundations but also by driven piles. For three dimensional analysis of the huge and thick concrete structure, a solid-shell element that is capable of exact modeling and node interpolations of stresses is developed. By applying wave theory of stream function and solid-shell element in XSEA simulation software for fixed offshore wind turbines, a quasi-static analysis and natural frequency analysis of proposed support structure are performed with the environmental condition on Southwest Coast in Korea. In the result, lateral displacement is not exceed allowable displacement and a superiority of dynamic behavior of new hybrid support structure is validated by natural frequency analysis. Consequently, the hybrid support structure presented in this study has a structural stability enough to be applied on real-site condition in Korea. The optimized structures based on the preliminary design concept resulted in an efficient structure, which reasonably reduces fabrication costs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.3
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• pp.1288-1295
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• 2012

Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WP's turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP's Generator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling.